It is known in the prior art of plastic sheet roofing to apply panels of sheet material, for example each about 2 feet wide, in overlapping relationship, with spaced hold-down plates, themselves secured to the roof with screws, along an edge of each panel, spaced inwardly therefrom to permit then a heat seal to an adjoining panel along the edge.
A problem has been that lift forces on the panels in consequence of wind blowing past the panels has resulted in central portions of the panels lifting up from the roof, bending the hold-down plates, and imposing peel forces on the heat seals between panels, all of which conduce unduly to failure.